Within electrical networks contactors are often used for switching large electric currents. These contactors are designed for switching load currents that occur during normal conditions in various applications. The contactor is designed so as to be able to make, conduct and break the electric current.
Electromagnetically operated contactors typically comprise a spring-biased armature moving between two end positions. The armature is a part of an electromagnetic circuit. At a first end position the armature is open and the current path is then open, and at a second end position, the armature is closed and the contactor is then closed, thereby providing an electrical path. Normally contactors are monostable devices and the position of rest is the open position but the opposite positions are sometimes used. At the first end position there is thus no electric path and the electric circuit is open, at the second position the electric path is closed and the electric circuit is then closed. The movement of the armature is accomplished by energizing a coil of the electromagnetic circuit, the coil typically being wound around parts of either the armature or around a fixed part of the electromagnetic circuit.
Operation of such contactor entails applying a current to the coil, whereby a magnetic flux is produced in the electromagnet. The magnetic flux attracts the armature, which forces contacts of the contactor to close. Contactors need high coil current during closing (often also called “making” or “make”), since an air gap between two magnet parts of the electromagnet is large and the spring force of springs in the armature needs to be overcome. When holding the contactor closed, denoted “hold state”, the air gap is small and a low coil current is sufficient.
In order to secure reliable contact making, a high current is applied to the coil for a fixed period of time including a safety margin, before switching to the hold state with low current. The application of high current during the closing creates losses and increased temperature in the coil, and the period with high current after the contactor has closed results in wasted energy. The wasted energy corresponds to unnecessary additional supply power, with entailing increased costs. Operating energy is often supplied by sources with limited capacity and therefore it is desired to minimize the energy used. The wasted energy also increases the temperature in the coil as well as in other electronics, which may adversely affect their functionality and reduce their operational time.